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      <title>3、Oracle对象 - 交互式测验</title>
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          <div class="quiz-container">
            <div class="quiz-header">
              <h1>3、Oracle对象 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
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      <script>
        const quizData = [
  {
    "question": "根据文档，当一个表被 `DROP TABLE` 命令删除后，Oracle 的 \"闪回技术\" (Flashback) 提供了什么核心功能？",
    "options": [
      "永久性地清除表以释放磁盘空间。",
      "回滚当前事务中对表的所有未提交更改。",
      "将被删除的表从回收站（recyclebin）中恢复。",
      "为被删除的表创建一个完整的备份文件。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档中明确指出，“闪回技术就是将删除的表恢复”。Oracle 会将被 `DROP` 的表放入一个名为 `recyclebin` 的特殊区域（类似于操作系统的回收站），而不是立即永久删除。通过 `FLASHBACK TABLE 表名称 TO BEFORE DROP` 命令，可以将这个表从回收站中恢复回来。",
    "source": "文档中「1.7 闪回技术」部分",
    "hint": "文档中提到，被删除的表会存放在一张特殊的表中，这张表就类似于“回收站”。"
  },
  {
    "question": "在事务的四大特性（ACID）中，哪一个特性保证了事务一旦提交，其对数据库的修改就不会丢失，即使系统发生故障？",
    "options": [
      "原子性 (Atomicity)",
      "一致性 (Consistency)",
      "持久性 (Durability)",
      "隔离性 (Isolation)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "持久性（Durability）是ACID模型中的关键特性，它确保了任何已提交的事务对数据库所做的更改都是永久性的。即使在系统崩溃或断电等故障发生后，这些已提交的更改也不会丢失，数据库能够恢复到事务成功提交后的状态。",
    "source": "文档中「4.1 事务四大特性(简称ACID)」部分",
    "hint": "这个特性的描述是：“对于任意已提交事务，系统必须保证该事务对数据库的改变不被丢失...”。"
  },
  {
    "question": "在 Oracle 数据库中，如果需要从名为 `user_id_seq` 的序列（SEQUENCE）中获取下一个可用的唯一编号，应该使用哪个关键词？",
    "options": [
      "user_id_seq.currval",
      "GET NEXT FOR user_id_seq",
      "user_id_seq.nextval",
      "AUTO_INCREMENT(user_id_seq)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档明确指出，`序列名称.nextval` 用于获取序列的下一个值。每次调用 `nextval`，序列的当前值都会按照定义的步长增加，并返回这个新的值。而 `currval` 则是用来获取当前会话中最后一次调用 `nextval` 所返回的值，它不会改变序列的值。",
    "source": "文档中「6.3 使用序列」部分",
    "hint": "文档中描述了两种使用序列的方式，一种是获取“下一次增长”，另一种是获取“当前序列值”。"
  },
  {
    "question": "根据文档对视图（View）的描述，以下哪项是关于视图最准确的陈述？",
    "options": [
      "视图是一个或多个表的逻辑表示，它本身不存储实际数据。",
      "视图是基表的一个完整物理副本，主要用于数据备份。",
      "对视图的所有修改操作（增、删、改）都会被数据库禁止。",
      "视图只能基于单个表创建，不能关联多个表。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "文档定义视图为“基于一个表或多个表或视图的逻辑表，本身不包含数据”。它本质上是存储在数据字典里的一条 `SELECT` 语句，提供了一种访问和操作基表数据的窗口，但数据本身仍在基表中，视图本身并不占用数据存储空间。",
    "source": "文档中「5. 视图」部分",
    "hint": "思考一下视图的定义：“视图是......的逻辑表，本身不包含数据”。"
  },
  {
    "question": "在 Oracle 数据库约束中，哪种约束用于确保字段中的值满足用户自定义的逻辑条件（例如，`age BETWEEN 0 AND 200`）？",
    "options": [
      "唯一约束 (UNIQUE)",
      "检查约束 (CHECK)",
      "主键约束 (PRIMARY KEY)",
      "非空约束 (NOT NULL)"
    ],
    "correctAnswerIndex": 1,
    "explanation": "检查约束（CHECK）允许用户定义一个布尔表达式，每一行数据在插入或更新时都必须使该表达式的计算结果为 TRUE，否则操作将失败。这常用于强制执行业务规则，如文档中 `check(age between 0 and 200)` 的例子，确保了年龄数据的有效性。",
    "source": "文档中「2.4 检查约束(CK)」部分",
    "hint": "这种约束被描述为“用户自行编写设置内容的检查条件”。"
  },
  {
    "question": "文档介绍了 ROWNUM 和 ROWID 两个伪列，它们的主要区别是什么？",
    "options": [
      "ROWID 和 ROWNUM 都是记录的物理地址，只是编码方式不同。",
      "ROWID 是查询结果集的动态行号，而 ROWNUM 是每条记录唯一的物理地址。",
      "ROWID 是每条记录唯一的物理地址标识，而 ROWNUM 是查询结果集的动态行号。",
      "ROWNUM 是一个可以被 `UPDATE` 语句修改的列，而 ROWID 不能。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "`ROWID` 是一个永久性的、唯一标识数据库中某条记录物理位置的字符串，它不存储在表中但可以被查询。而 `ROWNUM` 是一个临时的伪列，它是在查询执行过程中为返回的每一行动态分配的、从1开始的序列号，常用于分页查询。",
    "source": "文档中「7.1 ROWID伪列」和「7.2 ROWNUM伪列」部分",
    "hint": "一个被描述为“唯一标识一条记录物理位置的一个ID”，另一个被描述为“一个数据行编号的伪列...为用户动态分配一个数字”。"
  },
  {
    "question": "如果需要为一个已存在的表 `T_USER` 添加一个新的、用于存储密码的字段，应该使用以下哪条 SQL 命令？",
    "options": [
      "ALTER TABLE T_USER ADD (password VARCHAR2(50));",
      "MODIFY TABLE T_USER ADD COLUMN password VARCHAR2(50);",
      "UPDATE T_USER ADD (password VARCHAR2(50));",
      "CREATE COLUMN password ON T_USER (VARCHAR2(50));"
    ],
    "correctAnswerIndex": 0,
    "explanation": "`ALTER TABLE` 是用于修改已存在表结构的 DDL (数据定义语言) 命令。`ADD` 子句专门用于向表中添加新的列。文档中给出的正确语法是 `ALTER TABLE 表名称 ADD (字段名称 字段类型 ...)`。",
    "source": "文档中「1.8.1 表中添加字段」部分",
    "hint": "文档中修改表结构的相关命令是以 `ALTER TABLE` 开头的。"
  },
  {
    "question": "在Oracle中，为了存储海量的文字信息，例如一篇文章或者一篇长篇评论，文档推荐使用哪种数据类型？",
    "options": [
      "VARCHAR2(4000)",
      "CHAR(2000)",
      "BLOB",
      "CLOB"
    ],
    "correctAnswerIndex": 3,
    "explanation": "文档中的数据类型表明确指出，CLOB（Character Large Object）类型“用于存放海量的文字”。虽然 VARCHAR2 也可以存字符串，但它有长度限制（通常是4000字节），而 CLOB 设计用于存储非常大的文本数据，可以达到几个GB。",
    "source": "文档中「1.2 Oracle中常用的数据类型」部分",
    "hint": "在数据类型表格中，寻找描述为“用于存放海量的文字”的类型。"
  }
];
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            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

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                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  